In a cooking pot or heavy indian kadai(wok), add the mustard oil and warm on low medium heat until its slightly smoky.
Carefully slide the poatoes into the oil and sprinkle a pinch of salt. Brown the poatoes on all the sides. Do not cook them through. Add the dal wadi for few seconds to the hot oil once you are about to take out the potatoes. Wadis burn in no time so we just need to shallow fry for 12-15 seconds. Once browned, take potatoes & wadi in a bowl.
Remove the pot from stove. Temper the remainng oil with bay leaf, green cardamom and cloves. Add hing, green chilies, garlic paste and chopped ginger. Saute for 5-7 seconds, be careful the spices might pop. Return the pot back to stove. Add the chopped onions next and on low medium heat brown the onions stirring regularly to a nice golden color.
Next, add all the ground spices. Add 2-3 tablespoons of water Fry in oil for 10-15 seconds. Don't let burn.
Add the tomatoes and pinch of sugar next. Fry for 5-6 minutes on low medum heat until you see that the masala is deep in color and the oil is seperating.
Add the ground peas now along with reserved whole peas & more julinned ginger(if using) and mix well with the masala. Fry everything on low medium flame for good 7-9 minutes, scrapping the sides and bottom of pan since the peas have a tendency to stick. The peas will slowly start turning brown. Keep on frying till you see that the peas are lightish brown and a bit shiny. This bhunai is one of the key steps in developing deep flavors in nimona. You may add 1-2 tablesoons of ghee during bhunai if you desire.
Once the peas are browned, add about a cup and a half of warm water. Add the potatoes, dal wadi & chopped ilantro as well as well. Mix everything, it should be a thick curry right now. Taste and adjust the salt.
Bring to a slight boil, cover with a lid, reduce the stove to low and let simmer for 12-14 minutes or untill the potatoes are fork tender. If you feel that the nimona is getting too thick, add ¼ cup or more hot water. Simmer again after you add water. Don't make very watery though. You will see a little thin layer of oil on top by the end.
Mix in the amchoor and roasted cumin powder. Nimona is ready.
Add the tempering(if using). Mix well. Cover and let rest for atleast 30 minutes before serving.